1. Field of the Invention
The present invention relates to intake valves for internal combustion engines. More particularly, this invention pertains to an intake valve that includes a floating valve seat.
2. Description of the Prior Art
Among the most critical elements of an internal combustion engine are the valves that regulate the gas flow into and out of the combustion chambers. Each chamber houses a reciprocating piston. Thus, for example, an eight cylinder engine has eight pistons requiring the careful regulation of sixteen valves (assuming two valves per cylinder).
The output of the engine consists of rotation of a crankshaft. This is distributed to the wheels by means of a differential engaged to an axle. Rotation of the crankshaft is produced through successive, phased inputs of angular motion via connecting rods pivotally engaged at one end to pistons, and, at the other, to rod journals which are often offset from the main journals that lie along the axis of rotation of the crankshaft. The application of successive, phased forces to the offset journals results in crankshaft rotation.
The axis of rotation of the crankshaft is aligned with that of a drive shaft that can be engaged and disengaged from the crankshaft by means of a clutch. The output of the drive shaft is, in turn, employed, to drive the wheels of the vehicle through the differential.
Thus, an internal combustion engine translates the reciprocating motions of the pistons into rotation of a shaft. The generation of the reciprocating movements of the pistons is accomplished through the well-understood four-stroke process of internal combustion known as the Otto cycle. The four elements of this process include an xe2x80x9cintake strokexe2x80x9d during which a mixture of air and fuel is received at the top of the combustion chamber (i.e. above the piston) from a carburetor or fuel injectors. The piston travels downwardly (pulled by the rotating crankshaft via the connecting rod), creating a vacuum that sucks in the air-fuel mixture. After the intake stroke, the portion of the combustion chamber above the piston is sealed by the closure of an intake valve and a xe2x80x9ccompression strokexe2x80x9d is commenced during which the connecting rod pushes the piston upwardly, compressing the air-fuel mixture. Once the compression stroke has been completed, a high-voltage spark is emitted by a spark plug, igniting the air-fuel mixture within the sealed combustion chamber. The resulting combustion of the mixture causes an expansion of gaseous volume, generating a force that acts downwardly upon the top of the piston during a xe2x80x9cpower strokexe2x80x9d. This drives the piston down to impart rotation to the crankshaft. The amount of angular motion imparted is, in part, dependent upon the number of engine cylinders. Once this motion has been completed, the gases within the combustion chamber are vented during an xe2x80x9c-exhaust strokexe2x80x9d as the piston is again driven upwardly within the cylinder by the rotation of the crankshaft and the exhaust valve that regulates the passage of gases through an exhaust port is opened. Another four-stroke cycle then begins with another intake stroke in which air-fuel mixture is admitted through a reopened intake valve and the exhaust valve is closed. At a typical freeway engine speed of 2200 r.p.m., the entire four-stroke process is completed at a rate of eighteen times per second in each cylinder.
Intake and exhaust ports communicate with the portion of the cylinder that lies above top dead center of the piston (i.e., the combustion chamber). The intake and exhaust valves seal the head ports. The motions of the valves are derived from the crankshaft of the engine through a valve train linkage that includes the valve itself.
The valves include elongated stems and terminate in generally-circular broadened heads that include angled faces cut to match an angle formed by a head seat formed within the engine head. The head seats and poppet-type valves interact whereby the combustion chamber is opened to communicate with the intake and/or exhaust ports by the action of the valve train pushing down on the valves and then closed by a spring, a side component of the valve train. The spring returns the valve (stem protruding from the combustion chamber of the head to the rocker assembly side of the head) until its enlarged head abuts the head seat adjacent the top of the combustion chamber. A seal is formed between the circumferential face of the valve and the circular head seat. Conversely, an intake valve admits a gaseous mixture when driven downwardly to disengage the valve face from the head seat located in the combustion chamber of the engine head.
The cam of the valve linkage that defines the relationship between rotation of the crankshaft (and, thus travel of the piston within the cylinder) and the opening and closing of the intake and exhaust valves is of static design. Since the cam possesses a static, fixed shape, the relative timing of the opening and closing of the valves with respect to the travel of the piston within its cylinder is correspondingly limited or static.
The mass, and resulting momentum and inertia, of the valve train constrains the ability of the engine to operate in an idealized manner insofar as the coordination of valve operation and piston movements within the combustion chamber. For example, a typical profile of the intake stroke might consist of the cam gear gradually opening the inlet valve by one-eighth inch upon the piston having.traveled downwardly by two inches, then increasing to one quarter inch when piston travel has increased to three inches, then continuing to be held open by one-quarter inch during the fourth inch of travel of the piston. The valve might then begin to close during the interval between the fourth and fifth or final inches of downward travel of the piston. This would occur in anticipation of its imminent closure for the subsequent compression stroke.
Such xe2x80x9cpreparationxe2x80x9d of the valve for closure during the transition from the intake to the compression stroke, built into the shape of the cam, is an acknowledgment of the inability of the valve train to reverse direction instantaneously in view of its mass. The non-idealized operation of the valve with respect to the movement of the piston within the combustion chamber has the effect of either forcing some amount of the fresh air-fuel mixture out of the chamber through the intake port (in the event that the point of closure of the intake valve occurs after the direction of the piston has reversed) or the admission of a less-than-maximum amount of air-fuel mixture into the chamber (in the event that the point of closure occurs somewhat prior to completion of downward travel of the piston). In either event, the torque generated by the engine is reduced below that theoretically possible with a valve linkage of zero mass.
An additional practical limitation upon valve operation is crankshaft rotation rate (in r.p.m.). Practical cam design requires more gradual transitions between valve openings and closings at a high r.p.m. engine output to prevent risk of valve train element disengagements. The resultant gradual reversals of valve direction further reduce the torque that may be generated by an internal combustion engine through reduction and/or contamination of intake of fresh air-fuel mixture and loss of compression.
Like issues pertain to the transition from the exhaust to the intake strokes. The exhaust valve, symmetrically located at the top of the combustion chamber with respect to the intake valve, undergoes closure during this transition. In the event that the intake valve, making a transition from a closed to an open attitude as the piston rises to the top of its travel, opens xe2x80x9cearlyxe2x80x9d (before the exhaust valve has closed and the piston reached the top of the chamber, a condition known as xe2x80x9coverlapxe2x80x9d), exhaust gases can escape from the chamber through the slightly open intake valve and into the intake port (a condition known as xe2x80x9creversionxe2x80x9d). This will contaminate the fresh air-fuel mixture admitted during the intake stroke. Conversely, should the intake valve open xe2x80x9clatexe2x80x9d (after the exhaust valve has closed and the piston has already begun downward travel), less than the theoretically-possible maximum amount of air-fuel mixture will enter the cylinder during the intake stroke. In either case, the torque generated during the following power stroke is ultimately reduced.
One approach to the above-described problems of static valve timing is a device marketed under the trademark SMART VALVE by Acro-Tech, Inc. which is described in xe2x80x9cVariable Valve Timingxe2x80x9d, American Iron Magazine (September 2000) at page 135. Such device comprises an intake valve, suitable for retrofitting to a four cycle engine, that is characterized by a two-part valve head structure. Such structure consists of a valve head base and a surrounding peripheral ring. The valve head base comprises an otherwise-conventional valve head machined to accommodate the peripheral ring in slidable, locking relationship. The precise vertical position of the peripheral ring is responsive to gas pressure within the combustion chamber. When actuated by gas pressure to travel upwardly either at the beginning of the compression stroke or at the transition from exhaust stroke to intake stroke, the peripheral ring, in combination with the valve head base, seals the intake port prior to the time otherwise dictated by the fixed shape of the cam. This results in a type of variable valve timing in which loss or contamination of air-fuel mixture and/or compression loss is minimized and engine torque is thereby increased.
While offering a useful concept, the precise design of the device described above is subject to a number of weaknesses. The design permits a continuous escape of gases through actuation port holes when the ring is in the lifted position due to the location of the lock mechanism. In addition, the location of the locking mechanism for slidably securing the peripheral ring to the valve head base (in the region of the margin of the valve head), limits the ability of a designer to increase the vertical travel of the peripheral ring without increasing the mass of the valve head and ring. Finally, the positioning of the locking mechanism subjects potential areas of weakness to maximum stressing and permits the cocking of the peripheral ring with respect to the axis of the valve, permitting the peripheral ring""s locking lip to drag against the valve head margin area, increasing wear. The mating areas will allow excessive use to hammer the peripheral ring below its desired seating position. The design also incorporates knife edges on the ring that are susceptible to abuse.
The invention addresses the preceding and other shortcomings of the prior art by providing, in a first aspect, an intake valve for an internal combustion engine. The valve includes an elongated valve stem having opposed ends. A valve head base is located at one end of and integral with the valve stem. A peripheral ring is provided.
The valve head base includes a region adapted to receive the peripheral ring in vertically-actuable relationship. The peripheral ring includes an inner vertical portion and an outer, inclined valve seat. The region of the valve head base for receiving the peripheral ring includes an inner vertical portion in opposed relationship to the inner vertical portion of the peripheral ring.
The inner vertical portion of the peripheral ring has an inwardly-directed annular flange and the inner vertical portion of the region of the valve head base has an outwardly-directed annular flange for slidably locking the peripheral ring to the valve head base.
In a second aspect, the invention provides an internal combustion engine that includes an intake valve in accordance with the embodiment described above.
In a third aspect, the invention provides an intake valve for an internal combustion engine. The valve includes an elongated valve stem having opposed ends. A valve head base is located at one end of and integral with the valve stem. A peripheral ring is provided.
The valve head base includes a region adapted to receive the peripheral ring in vertically-actuable relationship. The peripheral ring includes an inner vertical portion and an outer, inclined valve seat. The region of the valve head base includes an upwardly-convex surface.
The peripheral ring includes a downwardly-concave base surface. The upwardly-convex and downwardly-concave surfaces are arranged to mate when the peripheral ring is in a non-actuated state.